To produce flour, grain may be fed between two elongated grinding cylinders separated by a specified distance or gap. The milling process may consist of different grinding stages depending on the desired grind of the final product. During the milling process, the grinding cylinders are subject to wear and must be adjusted to maintain the desired gap. A first grinding cylinder axis may be fixed in position while a second grinding cylinder axis is adjustable.
Conventional flour mill roll stands are equipped with oil lubricated gear boxes and utilize change gears to maintain the gap when grinding cylinders wear. A grinding cylinder drive gear may be repeatedly changed for a smaller drive gear to reduce the distance between the grind cylinder axes and thus reduce the gap between the grinding cylinders. In general, millers may change the drive gear up to eight times before replacing a grinding cylinder. Fine adjustments are achieved before replacing a drive gear by moving the adjustable axis of the first grinding cylinder closer to the fixed axis of the second grinding cylinder. The respective drive gears of the first and second grinding cylinders are also moved closer together as a result. Consequently, the drive gears are running outside of the optimal pitch line approximately 90% of the time, thus causing premature gear wear. Regular adjustment to gear position also results in gear box seal leaks.
To overcome the problems associated with gear driven roll drives, belt drives and chain drives have been employed. The use of change gears may be avoided, but belts are subject to high tension and may break without warning requiring emergency repair. Belts must also be tensioned after each adjustment requiring the mill to stand still. Chains experience similar problems as belts and additionally must be lubricated.